1. Field of the Invention
The present invention relates to an authenticity indicator to be used to indicate that an article or the like is authentic, and particularly to an authenticity indicator whose authenticity can be checked easily and accurately. The present invention also relates to an authenticity checking method for checking the authenticity of an authenticity indicator to be used to indicate that an article or the like is genuine, and an authenticity checking system useful for checking the same, and particularly to an authenticity checking method and system by which the authenticity of the authenticity indicator can be checked easily and accurately.
2. Related Art
Hologram labels, etc. using holograms, serving as authenticity indicators (identification media), have been attached to genuine articles as a means of preventing forgery of cards, passports, ID cards, gift certificates, etc., or of detecting forgeries, fakes, or the like. It is therefore essential for the authenticity indicators that they are difficult to be forged and that the authenticity of the authenticity indicators themselves can be checked accurately.
In recent years, however, techniques for forgery of holograms of this type have advanced, and holographic materials have become easily available, so that there are possibilities that the hologram labels might be skillfully forged and that the forged hologram labels might be overlooked while they are practically used.
Cholesteric liquid crystals, which have both polarized-light selectivity and wavelength selectivity and reflect light so that the reflected light changes in color when an observer changes his viewing angle, have also been used for authenticity indicators. However, forgery techniques have advanced in recent years, and even authenticity indicators using cholesteric liquid crystals are in danger of forgery.
Authenticity indicators using holograms and cholesteric liquid crystals in combination are now being developed (e.g., Japanese Patent Publication No. 3652487 and Japanese Laid-Open Patent Publication No. 2000-211300).
Japanese Patent Publication No. 3652487 discloses an authenticity indicator using a relief hologram layer and a cholesteric liquid crystal layer in combination. In this authenticity indicator, the cholesteric liquid crystal layer is used as a layer for reflecting the relief hologram. Since relief holograms are relatively easy to be forged, the authenticity indicator disclosed in this patent publication can only have a forgery preventing effect comparable to that of an authenticity indicator using a cholesteric liquid crystal layer alone.
Japanese Laid-Open Patent Publication No. 2000-211300 discloses an authenticity indicator using a reflection hologram layer and a cholesteric liquid crystal layer in combination. In this authenticity indicator, the cholesteric liquid crystal layer serves as a layer for reflecting light that has passed through the reflection hologram without being diffracted by it. The reflection hologram layer diffracts (reflects) only light with wavelengths in a narrow wavelength range centering around a specified wavelength, responding to the wavelength selectivity of the reflection hologram. This authenticity indicator is therefore disadvantageous in that it is difficult to confirm the authenticity of the authenticity indicator by the diffracted light from the reflection hologram layer, or that an expensive device such as a highly sensitive light-receiving unit is needed for authenticity checking.